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[SVC34-P01] Lava cave formation and temperature of 1951 Eruption of Miharayama in Izu-Ooshima
Keywords:lava cave, lava tube, lava flow, Miharayama, lava yield strength, lava temperature
[Introduction]
Two lava caves (Mihara Wind Cave and Mihara Hornito Cave) were formed by the 1951 eruption of Miharayama on Izu Oshima. Mihara Wind Cave [1-3] are located on the edge of the north-northeast crater wall of Izu Oshima, and Mihara Hornito Cave [4-6] is located on the west edge of the crater wall in Izu Oshima. Mihara Wind Cave was clearly observed by Tsuya et al. [1] and surveyed by Katsumata [3], but it was buried by the lava flow of the 1986 eruption. As for Mihara Hornito Cave ,it is recognized that the Mihara Hornito is likely to have a cavity under the Hornito. However, it was prevented from being buried by the lava flow of the 1986 eruption. Observations and measurements of the interior were first carried out by Tachihara et al. [4] in 2005. On the other hand, the flow velocity, lava flow thickness, temperature, etc. of the lava flow that overflowed from the crater were precisely recorded by Minakami [7]. ,Compared with those data, we considered lava cave formation process and its temperature.
[Mihara Wind Cave]
Figure 1 is a survey map of Mihara Wind Cave, and Photos 1 to 3 show the inside and opening [3]. There are no lava stalactites or lava stalagmites inside, but lava shelves can be seen [1]. Mihara Wind Cave exists on a flat area at the edge of the crater, and no tube-shaped cavity has been found in the down stream.This is probably because the lava inside after the lava expanded drained back into the crater, and lava tube was not formed in downstream.
[Mihara Hornito Cave]
Figure 2 shows a survey map of Mihara Hornito Cave [4-6], Photo 4 shows the inside of the flat part of the crater wall, and Photo 5 shows the inside of the sloping tube-shaped downstream part. Photo 6 shows the outside appearance of Hornito. The height of the cavity from the flat part P1 to P0 of the Mihara Hornito Cave in Figure 2 is at most 4 to 5 m, which is thought to have been caused by the expansion of the lava flow. It is thought that the soft lava inside was discharged through the tube with a cavity height of H= 1.0 to 3.0 m at 17.3 degree slope from P0 to the downstream P4, and a height of H = 1.0 to 0.5 m on a slope of 28.7 degrees from P4 to P5 at the downstream end. From the cavity height(H=2R) of the lava tube and its inclination angle, the flow limit condition for Bingham fluid flowing in an inclined circular tube is fB=H(ρg sinα)/4,where H=2R [8], and the lava yield strength fB is 5500~1830Pa for 17.3 degree slope with ρ=2500kg/m3. From a slope of 28.7 degrees, the yield strength of 1,500 to 2,950 Pa can be obtained [9]. Since soft lava inside a hard shell appears to have been discharged from the tube at a slope of 28.7 degrees, by using a yield strength of 1500 to 2950 Pa, the temperature obtained from the temperature dependence equation for yield strength [9, 10] is estimated to be 1034 to 1068 °C. Both the yield strength and the temperature shown in Table 1 are approximately within the range of lava flow data [7, 11].
[Summary]
The temperature at which the tube cavity formed in Mihara Hornito Cave is estimated to be 1034-1068℃. This is consistent with the temperature of the lava flow that overflowed from the crater, which was 1125-1038℃ [7]. In Mihara Hornito Cave, the lava flow was formed in the horizontal part of the edge of the crater wall. It is thought that the lava expanded, and while the temperature decreased somewhat, the inside was drained out through the downstream by tube, forming a cavity (Figure 3). It is thought that the Mihara Wind Cave also formed a cavity when the lava expanded and the internal lava either drained back into the crater or was discharged downstream (Figure 3).
References:
[1] H. Tsuya, R. Morimoto, J. Ossaka (1955): University of Tokyo Earthquake Research Report No. 33 (1), p79-107, [2] T. Ogawa (1988): Japanese volcanic caves, Dojin, Volume 7, No. 3, [3] T,Honda, K.Suzuki, K.Kawamura (2023) Caving Journal, No. 77, p41, [4] H.Tachihara, O.Oshima, T.Honda (2006): Volcanic cave survey and observation report in Oshima Town, Tokyo, Volcano- Speleological Society, [5] T.Honda (2006): V102-001, Japan Geoscience Union Abstracts, [6] T.Honda et al. (2006): Caving Journal, No. 27, p32, [7] T. Minakami (1951): University of Tokyo Earthquake Research Bulletin 29,487, [8] T.Honda (2001): B10, the Volcanology Society of Japan Programme and Abstract 2001(2), p66, [9] T.Honda, J.Haruyama (2020): 3E11, 64th Space Science and Technology Union Meeting, [10] K.Ishihara, M.Iguchi, K.Kamo (1988): Kazan, Vol. 2, Volume 33, Izu Oshima Eruption Special Issue, S64, [11]T.Honda (2022), P1-39, Volcanological Society of Japan 2022 Fall Meeting.
Two lava caves (Mihara Wind Cave and Mihara Hornito Cave) were formed by the 1951 eruption of Miharayama on Izu Oshima. Mihara Wind Cave [1-3] are located on the edge of the north-northeast crater wall of Izu Oshima, and Mihara Hornito Cave [4-6] is located on the west edge of the crater wall in Izu Oshima. Mihara Wind Cave was clearly observed by Tsuya et al. [1] and surveyed by Katsumata [3], but it was buried by the lava flow of the 1986 eruption. As for Mihara Hornito Cave ,it is recognized that the Mihara Hornito is likely to have a cavity under the Hornito. However, it was prevented from being buried by the lava flow of the 1986 eruption. Observations and measurements of the interior were first carried out by Tachihara et al. [4] in 2005. On the other hand, the flow velocity, lava flow thickness, temperature, etc. of the lava flow that overflowed from the crater were precisely recorded by Minakami [7]. ,Compared with those data, we considered lava cave formation process and its temperature.
[Mihara Wind Cave]
Figure 1 is a survey map of Mihara Wind Cave, and Photos 1 to 3 show the inside and opening [3]. There are no lava stalactites or lava stalagmites inside, but lava shelves can be seen [1]. Mihara Wind Cave exists on a flat area at the edge of the crater, and no tube-shaped cavity has been found in the down stream.This is probably because the lava inside after the lava expanded drained back into the crater, and lava tube was not formed in downstream.
[Mihara Hornito Cave]
Figure 2 shows a survey map of Mihara Hornito Cave [4-6], Photo 4 shows the inside of the flat part of the crater wall, and Photo 5 shows the inside of the sloping tube-shaped downstream part. Photo 6 shows the outside appearance of Hornito. The height of the cavity from the flat part P1 to P0 of the Mihara Hornito Cave in Figure 2 is at most 4 to 5 m, which is thought to have been caused by the expansion of the lava flow. It is thought that the soft lava inside was discharged through the tube with a cavity height of H= 1.0 to 3.0 m at 17.3 degree slope from P0 to the downstream P4, and a height of H = 1.0 to 0.5 m on a slope of 28.7 degrees from P4 to P5 at the downstream end. From the cavity height(H=2R) of the lava tube and its inclination angle, the flow limit condition for Bingham fluid flowing in an inclined circular tube is fB=H(ρg sinα)/4,where H=2R [8], and the lava yield strength fB is 5500~1830Pa for 17.3 degree slope with ρ=2500kg/m3. From a slope of 28.7 degrees, the yield strength of 1,500 to 2,950 Pa can be obtained [9]. Since soft lava inside a hard shell appears to have been discharged from the tube at a slope of 28.7 degrees, by using a yield strength of 1500 to 2950 Pa, the temperature obtained from the temperature dependence equation for yield strength [9, 10] is estimated to be 1034 to 1068 °C. Both the yield strength and the temperature shown in Table 1 are approximately within the range of lava flow data [7, 11].
[Summary]
The temperature at which the tube cavity formed in Mihara Hornito Cave is estimated to be 1034-1068℃. This is consistent with the temperature of the lava flow that overflowed from the crater, which was 1125-1038℃ [7]. In Mihara Hornito Cave, the lava flow was formed in the horizontal part of the edge of the crater wall. It is thought that the lava expanded, and while the temperature decreased somewhat, the inside was drained out through the downstream by tube, forming a cavity (Figure 3). It is thought that the Mihara Wind Cave also formed a cavity when the lava expanded and the internal lava either drained back into the crater or was discharged downstream (Figure 3).
References:
[1] H. Tsuya, R. Morimoto, J. Ossaka (1955): University of Tokyo Earthquake Research Report No. 33 (1), p79-107, [2] T. Ogawa (1988): Japanese volcanic caves, Dojin, Volume 7, No. 3, [3] T,Honda, K.Suzuki, K.Kawamura (2023) Caving Journal, No. 77, p41, [4] H.Tachihara, O.Oshima, T.Honda (2006): Volcanic cave survey and observation report in Oshima Town, Tokyo, Volcano- Speleological Society, [5] T.Honda (2006): V102-001, Japan Geoscience Union Abstracts, [6] T.Honda et al. (2006): Caving Journal, No. 27, p32, [7] T. Minakami (1951): University of Tokyo Earthquake Research Bulletin 29,487, [8] T.Honda (2001): B10, the Volcanology Society of Japan Programme and Abstract 2001(2), p66, [9] T.Honda, J.Haruyama (2020): 3E11, 64th Space Science and Technology Union Meeting, [10] K.Ishihara, M.Iguchi, K.Kamo (1988): Kazan, Vol. 2, Volume 33, Izu Oshima Eruption Special Issue, S64, [11]T.Honda (2022), P1-39, Volcanological Society of Japan 2022 Fall Meeting.